Method of coating pipe with continuously reinforced concrete

ABSTRACT

A method of making a metal reinforcing strip suitable for use in reinforcing a coating applied onto a pipe comprising providing a strip of welded wire mesh having longitudinal and transverse wires, and passing the strip between a pair of rollers which deform the longitudinal wires to an extent which increases progressively across the strip.

This is a division of application Ser. No. 614,227, filed Sept. 17,1975, now U.S. Pat. No. 4,033,387.

The invention relates to a method of making a metal reinforcing stripfor use in reinforcing a coating applied to a cylindrical object, suchas a pipe.

It is sometimes necessary to apply a heavy coating of concrete or thelike to pipes for use underwater, for example oil pipelines, tocounteract their buoyancy. Such heavy coatings require reinforcement toenable them to withstand the pressures they encounter in use, and thereinforcing is usually provided by embedding metal reinforcing membersin the coating.

A concrete coating may be applied to a pipe by rotating the pipe and atthe same time moving it axially past a spraying station at whichconcrete is sprayed on the outer surface of the pipe. Simultaneouslywith the spraying, a metal reinforcing strip may be wound around thepipe and embedded in the concrete.

As the thickness of the concrete builds up on the pipe in the region ofthe spraying station it forms a generally frustoconical shape and then agenerally cylindrical shape. The reinforcing strip is applied in thefrustoconical region and hence one edge of the strip (that nearest thedirection in which the rotating pipe is axially moving) must surround alarger circumference than the other edge.

A known form of reinforcing strip for pipe coatings (see for exampleU.S. Pat. No. 3,761,557) comprises two or more longitudinal wires havingspaced-apart rods welded therebetween and wherein one of thelongitudinal wires is provided with a degree of slack between each pairof rods to allow it to expand when wrapped around a frustoconicalportion of a concrete coating. The manufacture of such a strip iscomplicated and difficult to achieve automatically because thelongitudinal wires must be supported and given the required amount ofslack and then the rods must be welded to the correct points of thewires. It is desirable to form a reinforcing strip from welded wire meshwhich is readily fabricated automatically.

According to the invention, there is provided a method of making a metalreinforcing strip comprising taking a strip of welded wire mesh havinglongitudinal wires and transverse wires, and deforming at least some ofsaid longitudinal wires to an extent which increases progressivelyacross the strip.

The longitudinal wires of the welded wire mesh are preferablysubstantially perpendicular to the transverse wires before deformation,such rectangular wire mesh being relatively easily fabricated andreadily available commercially.

The step of deforming at least some of the longitudinal wires may beperformed in a single operation by passing the strip of mesh between apair of rollers arranged to effect the said deformation of thelongitudinal wires. Preferably, however, the deforming step is performedin two operations; thus the strip of welded wire mesh may be passedbetween a pair of rollers arranged to deform to an equal extent all ofthe longitudinal wires of the mesh and subsequently passed between apair of rollers arranged to longitudinally expand the mesh to adifferent extent at different portions of its width.

Alternatively, the strip of welded wire mesh may be passed between apair of rollers arranged to deform to an equal extent all of thelongitudinal wires of the mesh and subsequently the mesh may be simplystretched or drawn to longitudinally expand the mesh to a differentextent at different portions of its width. The said stretching ordrawing may conveniently be carried out as the mesh is wound onto a pipein a coating operation.

The said longitudinal wires may be deformed so that they are bent butstill lie in the plane of the mesh. Preferably, however, they aredeformed in respective planes perpendicular to the plane of the mesh.This leads to improved keying with the coating and better reinforcementproperties.

The invention also provides a method of coating a pipe comprising thesimultaneous steps of rotating the pipe, spraying concrete onto theouter surface of the pipe, and winding onto the pipe a metal reinforcingstrip made by the method defined above.

Certain embodiments of the invention will now be described by way ofexample and with reference to the accompanying drawing, in which:

FIG. 1 shows a portion of a strip of welded wire mesh at an intermediatestage of a method according to the invention;

FIG. 2 shows the mesh of FIG. 1 being subjected to a further stage ofthe method and being wound on a pipe; and

FIG. 3 is a fragmentary longitudinal section of the coated pipe of FIG.2.

Referring now to the drawings, the method employs a strip ofconventional welded wire mesh, i.e. a mesh formed by welding straightparallel longitudinal wires to straight parallel transverse wires. Thelongitudinal wires are preferably substantially perpendicular to thetransverse wires. A convenient width of strip is from 150 to 250 mm.

In a first embodiment of the method, all of the longitudinal wires ofthe mesh are first deformed to the same extent. This can be done bypassing the welded wire mesh between a pair of suitably contouredrollers to form the mesh into the shape shown in FIG. 1. As can be seen,the longitudinal wires 2 of the mesh 1 are all deformed to the sameextent in respective planes perpendicular to the plane of the mesh.

The uniformly-deformed mesh 1 is then led to a coating station at whichit is passed between a pair of rollers 3 having inclined axes. Theserollers 3 serve to completely straighten out the deformations in thelongitudinal wire at one edge of the strip and to straighten out thedeformations in the other longitudinal wires to a progressively lesserextent across the width of the strip.

The reinforcing strip may now be wound around a rotating pipe withoutsubstantial further deformation, and simultaneously concrete or othersuitable coating material may be sprayed onto the outer surface of thepipe. The longitudinal wires with the greater deformations are arrangedto lie nearer the surface of the pipe as can be seen in FIG. 3, and thedecreasing extent of the deformations away from the surface of the pipeleads to good adhesion between the coating material and the reinforcingstrip.

As shown in the drawings, the longitudinal wires which are to lienearest the surface of the pipe may be formed closer together in thewire mesh than the other longitudinal area. This then prevents thedeformations in these longitudinal wires from being drawn out as thestrip is wound onto the pipe. Alternatively, the longitudinal wire whichis to be wound closest to the pipe surface could be stronger, as bymaking it of larger diameter than the other longitudinal wires or ofsquare cross-section but similar dimensions.

According to an alternative embodiment of the invention, theuniformly-deformed mesh 1 may be stretched or drawn to straighten outthe deformations in the longitudinal wires to a progressively lesserextent across the width of the strip. This may be done by omitting therollers 3 and allowing the rotating pipe to draw the wire mesh against abraking force applied to the spool from which the uniformly deformedmesh is fed or to the rollers which uniformly deform the mesh.

In another embodiment of the invention, the deformation of thelongitudinal wires may be performed in a single operation by passing thestrip between a single pair of rollers arranged so that the wire to belaid nearest the surface of the pipe receives the greatest deformation,while the wire at the other edge of the strip receives no or very littledeformation, the amount of deformation increasing progressively acrossthe strip.

We claim:
 1. A method of coating a pipe comprising the simultaneoussteps of rotating the pipe and moving it axially past a spraying stationspraying concrete onto the outer surface of the pipe and winding ontothe pipe a welded wire mesh comprising a plurality of longitudinal wiresand a plurality of spaced-apart transverse wires welded to saidlongitudinal wires, the length of longitudinal wire between adjacentones of at least some of said transverse wires being provided with auniform degree of slack across the width of said strip, and stretchingsaid mesh by means of the rotating pipe to longitudinally expand themesh to the extent that the slack varies progressively across the widthof said strip and one longitudinal side of the mesh forms a largerdiameter than the other longitudinal side thereof.
 2. A method ofcoating a pipe comprising the simultaneous steps of rotating the pipeand moving it axially past a spraying station spraying concrete onto theouter surface of the pipe, guiding towards the pipe a welded wire meshcomprising a plurality of longitudinal wires and a plurality of spacedapart transverse wires welded to said longitudinal wires, the length ofsaid longitudinal wires between adjacent transverse wires beingsubstantially straight across the width of said strip, providing saidlongitudinal wires between adjacent ones of at least some of saidtransverse wires with a uniform degree of slack across the width of saidstrip by deforming said longitudinal wires, and stretching said mesh bymeans of the rotating pipe to longitudinally expand the mesh to theextent that the slack varies progressively across the width of saidstrip and one longitudinal side of the mesh forms a larger diameter thanthe other longitudinal side thereof.
 3. A method of coating pipecomprising providing a welded wire mesh having a plurality oflongitudinal wires and a plurality of spaced-apart transverse wireswelded to said longitudinal wires, the length of longitudinal wirebetween adjacent transverse wires being substantially uniform across thewidth of said strip, simultaneously rotating the pipe and moving itaxially past a spraying station spraying concrete onto the outer surfaceof the pipe, deforming at least some of said longitudinal wires toproduce a deformation in said at least some of said longitudinal wireswhich deformation varies progressively across said strip, and windingthe welded wire mesh onto the pipe so that one longitudinal side of themesh forms a larger diameter than the other longitudinal side thereof.4. A method of coating a pipe as in claim 3 and wherein saidlongitudinal wires, prior to said deforming step, are substantiallyperpendicular to said transverse wires.
 5. A method of coating a pipe asin claim 3 and wherein said longitudinal wires are substantiallystraight prior to said deformation step.
 6. A method of coating a pipeas in claim 3 and wherein said deforming step is performed in a singleoperation by passing said welded wire mesh between a pair of rollersarranged to effect said deformation of the longitudinal wires,immediately prior to said winding step.
 7. A method of coating a pipe asin claim 3 and wherein the longitudinal wires are deformed in planessubstantially perpendicular to the plane of said strip.
 8. A method ofcoating a pipe as in claim 7 and wherein said longitudinal wires aresubstantially straight prior to said deformation step.
 9. A method ofcoating a pipe as in claim 7 and wherein said longitudinal wires have anundulated configuration in planes which are substantially perpendicularto the plane of said strip prior to said deformation step.
 10. A methodof coating a pipe as in claim 9 wherein said deforming step is performedas said welded wire mesh is being wound onto said pipe.